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ADVANCED MICRO SYSTEMS, INC. ADDENDUM
63
AMPS and Wire Count and Power
The rated current is specified based on the rated power input (watts) of a given motor.
A. Basic 8 Wire Motor
While never actually used as 8 individual coils, virtually all permanent magnet motors have 4 internal coils.
All common configurations can be constructed from the 8-wire motor.
Let us assume that each of 4 windings of the 8-wire motor has the
following specifications:
Current = 1 amps
Resistance =2.0 ohm (each of 4 coils)
Voltage= 2.0 volts
Inductance = 4.4 mH
The power per winding is:
I
2
R or 2 x 2 x 1= 4 watts,
x 4 coils = 16 watts total for this motor.
These values correspond closely with a NEMA size 23, 4 wire motor designs.
These following examples will configure the basic 8-wire motor into four real life connections:
4 Wire Parallel
The high-speed model implements parallel coil connection. Two coils
connected in parallel result in the following for each of the two phases:
Parallel Resistance= 1 ohms
Parallel Inductance= 2.2 mH
Current= 2.83 amps (8 watts/phase)
Watts per phase=8 (x 2 phases) = 16 watts total
B. 4 Wire Series
Changing to a series design, we have two pairs of two coils
connected in series. Each has:
Series Resistance= 4 ohms
Inductance= 17.5 mH
The rated current is now 1 amps (4 Volts)
Watts per phase=8 (x 2 phases) = 16 watts total
Note that the series inductance is FOUR times the parallel design.
Inductance limits the obtainable speed, since the time constant limits
the amount of flux (hence torque) when step-to-step time is short.
1
5
2
6
3
7
4
8
1B
1A
2A
2B
4 Wire Series
1
5
2
6
3
7
4
8
A Basic 8 Wire Motor
1
5
2
6
3
7
4
8
1B
1A
2A
2
B
4 Wire Parallel